tree-vrp.c (adjust_range_with_scev): When loop is not expected to overflow, reduce...

tree-vrp.c (adjust_range_with_scev): When loop is not expected to overflow, reduce overflow infinity to regular infinity.

./:	* tree-vrp.c (adjust_range_with_scev): When loop is not expected
	to overflow, reduce overflow infinity to regular infinity.
	(vrp_var_may_overflow): New static function.
	(vrp_visit_phi_node): Check vrp_var_may_overflow.
testsuite/:
	* gcc.dg/Wstrict-overflow-18.c: New test.

From-SVN: r125319